A) How does an altimeter work?
B) How do you calculate your Pressure Altitude?
First you need to know the current altimeter setting which you can get off the airport METAR. Now you need your International Standard Atmosphere pressure. Remember what that is? 29.92" of Mercury.
Now minus the current setting from the standard and see what you get. If the number is negative then minus that height from your elevation, if it's positive add it. For example:
Airport Elevation 2567 ft
Airport Altimeter 30.17
ISA Altimeter 29.92
29.92 – 30.17 = -0.25
Now it's just a case of getting the decimals in the right place. The far right digit is worth 10 feet the next 100 feet and the left of the decimal would be 1000 feet. It came out negative so we're going to minus
Our pressure altitude = 2567 – 250 = 2317 feet.
C) Will your altimeter over or under read if the pressure is dropping and you haven't adjusted the sub-scale?
With out any adjustments to your altimeter it will be over reading. For every 0.10" inches of mercury pressure change your altimeter will be wrong by 100 ft. For example:
Your altimeter on departure was 29.80". After flying for the afternoon you return to the airfield without adjusting to the new altimeter of 29.20". A difference of 0.60 or 600ft.
D) Your working in the Northern Domestic Airspace (NDA) 15nm from an airfield. What would your altimeter be set to?
See your AIM Section 2.10 for more information
E) What is Density Altitude?